This invention relates generally to an electrical connector assembly for interconnecting printed circuit boards. More specifically, this invention relates to a high speed, high density electrical connector assembly that provides improved cross-talk minimization and improved attenuation and impedance mismatch characteristics.
Electrical connectors are used in many electronic systems. It is generally easier and more cost effective to manufacture a system on several printed circuit boards (“PCBs”) which are then connected to one another by electrical connectors. A traditional arrangement for connecting several PCBs is to have one PCB serve as a backplane. Other PCBs, which are called daughter boards or daughter cards, are then connected through the backplane by electrical connectors.
Electronic systems have generally become smaller, faster and functionally more complex. This typically means that the number of circuits in a given area of an electronic system, along with the frequencies at which the circuits operate, have increased significantly in recent years. The systems handle more data and require electrical connectors that are electrically capable of handling the increased bandwidth.
As signal frequencies increase, there is a greater possibility of electrical noise being generated in the connector in forms such as reflections, cross-talk and electromagnetic radiation. Therefore, the electrical connectors are designed to control cross-talk between different signal paths, and to control the characteristic impedance of each signal path. In order to reduce signal reflections in a typical module, the characteristic impedance of a signal path is generally determined by the distance between the signal conductor for this path and associated ground conductors, as well as both the cross-sectional dimensions of the signal conductor and the effective dielectric constant of the insulating materials located between these signal and ground conductors.
Cross-talk between distinct signal paths can be controlled by arranging the various signal paths so that they are spaced further from each other and nearer to a shield plate, which is generally the ground plate. Thus, the different signal paths tend to electromagnetically couple more to the ground conductor path, and less with each other. For a given level of cross-talk, the signal paths can be placed closer together when sufficient electromagnetic coupling to the ground conductors are maintained.
Electrical connectors can be designed for single-ended signals as well as for differential signals. A single-ended signal is carried on a single signal conducting path, with the voltage relative to a common ground reference set of conductors being the signal. For this reason, single-ended signal paths are very sensitive to any common-mode noise present on the common reference conductors. It has thus been recognized that this presents a significant limitation on single-ended signal use for systems with growing numbers of higher frequency signal paths.
Differential signals are signals represented by a pair of conducting paths, called a “differential pair.” The voltage difference between the conductive paths represents the signal. In general, the two conducing paths of a differential pair are arranged to run near each other. If any other source of electrical noise is electromagnetically coupled to the differential pair, the effect on each conducting path of the pair should be similar. Because the signal on the differential pair is treated as the difference between the voltages on the two conducting paths, a common noise voltage that is coupled to both conducting paths in the differential pair does not affect the signal. This renders a differential pair less sensitive to cross-talk noise, as compared with a single-ended signal path.
One example of a differential pair electrical connector is shown in U.S. Pat. No. 6,293,827 (“the '827 patent”), which is assigned to the assignee of the present application. The '827 patent is incorporated by reference herein. The '827 patent discloses a differential signal electrical connector that generally utilizes individual shields corresponding to each pair of differential signals to provide shielding.
While the electrical connector disclosed in the '827 patent and other presently available differential pair electrical connector designs provide generally satisfactory performance, the inventors of the present invention have noted that at high speeds (for example, signal frequency of 3 GHz or greater), the presently available electrical connector designs may not sufficiently provide desired minimal cross-talk, impedance and attenuation mismatch characteristics.
These problems of cross-talk, impedance and attenuation mismatch are more significant when the electrical connector utilizes single-ended signals, rather than differential signals.
What is desired, therefore, is a high speed, high density electrical connector design that provides improved cross-talk minimization, impedance and attenuation control regardless of whether the connector utilizes single-ended signals or differential signals. Further, what is desired is a printed circuit board for such high speed, high density electrical connector design.